This course is run at the The University of Nottingham within the School of Computer Science & IT. The course is run by Graham Kendall (EMAIL : gxk@cs.nott.ac.uk)
If a page fault occurs it is better if there are plenty of free pages for the
page to be copied to. If we have the situation where every page is being used
we have to find a page to evict and we may have to write the page to disc before
evicting it.
Many systems have a background process called a paging daemon.
This process sleeps most of the time but runs at periodic intervals. Its task
is to inspect the state of the page frames and, if too few pages are free, it
selects pages to evict using the page replacement algorithm that is being used.
A further performance improvement can be achieved by remembering which page
frame a page has been evicted from. If the page frame has not been overwritten
when the evicted page is needed again then the page frame is still valid and
the data does not have to copied from disc again.
In addition the paging daemon, if it does not evict pages, can ensure they are clean. That is they have been written to disc so that if they are later evicted they can simply be overwritten without having to write data to disc.
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Last Updated : 23/01/2002